Stylish lets you customize any website with custom user styles (themes for websites). Choose from the largest userstyles library to change the color scheme, background, and skin for Google, Facebook, YouTube and many, many more sites.

Lightbeam is a Firefox add-on that enables you to see the first and third party sites you interact with on the Web. Using interactive visualizations, Lightbeam shows you the relationships between these third parties and the sites you visit.